Protective sleeves that are longitudinally opened are known to be used for surrounding elongated members and protect them from cuts, abrasion, radiant heat, vibrations, induced wear and other harsh environmental threats. The vibrations can lead to wear of the elongate members and, consequently of the sleeve itself. Such protective sleeves are also known for routing elongate members.
Besides this, such protective sleeves are used to absorb the noise arising from vibrations between cables, especially in automotive industry.
Protective sleeves that are longitudinally opened make easier their placement around cables to be protected. These protective sleeves, even though are longitudinally opened, are elastic in their behaviour and return back to their tubular shape automatically when they are in the rest position. These longitudinally opened sleeves are also known as “wrap-around” sleeve.
When positioning within protective sleeve, the wiring or cables are also held together in a neat bundle, allowing a multiplicity of different items to be handled as sub-assembly, thus saving time and effort during integration of the items into their environment.
Protective sleeves may be made by weaving or knitting yarns into a weaved or knitted textile and then resiliently biasing the two longitudinal free edges of said textile toward each other in order to impart a tubular form to the textile and to define an internal space for receiving elongate members. Biasing may be effected by heating the yarns in the final shape that is sought after. For example, biasing may be effected by heating the yarns when the textile is wrapped around a cylindrical mandrel or is placed in tubular form inside a tube, wherein the yarns take on a permanent set confirming to the shape of the mandrel or to the shape of the internal volume of the tube. The textile is then cooled down still wrapped around said mandrel or still disposed inside the internal volume of said tube. This thermo-forming step may be performed only if the sleeve comprises a monofilament yarn in a plastic material. This thermo-forming step imparts a shape memory or elastic memory to the textile and therefore to the sleeve. The textile used during this thermo-forming step is in the form of a strip in order to form a sleeve that has a longitudinally axis and a transverse axis, the length of the strip being higher than its width. The sleeve is heated at a temperature that is generally close to the glass transition temperature or the softening point of said plastic material(s). One example of a thermoforming step is described in U.S. Pat. No. 4,929,478, the description of which is incorporated herein by reference.
Monofilament yarns provide stiffness, and provide strong resilient biasing that maintains the textile in the tubular shape. The biased monofilaments also tend to restore the textile to its tubular shape in the absence of a distorting force, which is generally applied when the sleeve is manipulated to an open state to insert or remove an elongate member.
During this thermo-forming step, monofilament yarns in plastic material(s) shrink and form loops on the internal face or external face of the sleeve, especially when the textile is a warp-knitted textile and the monofilament yarns in plastic material(s) form laying-in stitches. These loops are unsightly and can be hooked by an elongate member during its insertion within the internal space of the sleeve when the loops are present on the internal face of the sleeve or can be hooked by other items disposed outside the sleeve when the loops are present on the external face of the sleeve. Moreover, these loops can wear the elongate members disposed within the internal space or items disposed outside the sleeve. These loops are even more developed when the sleeve comprises yarn(s) or is knitted on a substrate in a material that has a thermal behaviour that is different from the thermal behaviour of the plastic material(s) of the monofilaments yarns. The aforesaid loops could also be developed when the warp-knitted textile comprises multifilament yarns in glass or in an electrically conductive material or comprises yarns of different diameters or in different plastic materials.